1. Field of the Invention
The present invention relates to a microscopic image capturing apparatus, a microscopic image capturing method, and a storage medium recording a microscopic image capturing program, which shoot a sample image of a microscope by using an image capturing element such as a CCD, etc., and more particularly, to a microscopic image capturing apparatus, a microscopic image capturing method, and a storage medium recording a microscopic image capturing program, which store shading correction data created based on an externally input condition, and execute a shading correction process based on the shading correction data.
2. Description of the Related Art
Conventionally, a shading correction method and an image reading device, which modify read image data by making a shading correction for the read image data in order to remove noise superposed on the image data read by the image reading device used in a facsimile, a copier, an image scanner, etc., are known (for example, see paragraphs [0021] to [0028], and FIGS. 1 and 2 of Japanese Patent Publication No. HEI08-307674).
In the meantime, with a microscope, an enlarged light image of a sample was simply observed with an eyepiece lens in the past. However, in recent years, with a microscope, image data has been obtained by shooting an enlarged light image of a sample with an image capturing device, and the obtained image data has been displayed and observed on a display screen of an external device in many cases.
In such a case, an optical member such as an objective lens, a condenser lens, a TV adapter, etc, is replaced with a wide range of variations depending on an observation magnification of a microscope or an observation method in order to make an observation. At this time, a satisfactory shading characteristic cannot be always obtained due to a decrease in a marginal amount of light depending on a combination of an image capturing device and an optical member on the microscope side. If the above described shading correction is made for image data obtained by being shot with an image capturing device in such a case, a correction for the decrease in the marginal amount of light, etc., and noise removal can be made.
FIGS. 1A to 1F explain the above described conventional shading correction made to a captured microscopic image. For example, when a light image which is only illuminated without placing a sample on a stage (light image without a sample) is shot with a microscope, a phenomenon that the light image gradually becomes darker toward a marginal portion of the image as shown in FIG. 1A occurs as an undesirable shading characteristic.
If such a shading characteristic is left unchanged, also a sample image captured by placing the sample on the stage results in a similar image. Therefore, a shading correction process is executed in order to improve such a shading characteristic. To execute the shading correction process, shading correction data is first created.
The shading correction data is obtained by dividing the maximum value of pixel values within the image shown in FIG. 1A by each pixel value. If the largeness/smallness of the value of each pixel of the shading correction data is represented by light and dark, the data becomes the one shown in FIG. 1B, in which a dark portion in a central portion has, for example, a value “1”, and bright portions at the four corners have, for example, a value “1.5”. As described above, shading correction data is calculated from an image obtained by capturing a light image which is only illuminated without placing a sample in the capturing of a microscope image.
The pixel values of the image shown in FIG. 1A are multiplied by this shading correction data, so that the image can be converted into an image having even brightness as shown in FIG. 1C. Accordingly, also image data obtained from a sample image, which is acquired by capturing the image of a sample placed on a stage, can be converted into sample image data having even brightness with the shading correction process using the above described shading correction data.
Additionally, in a microscope, dirt, a blemish, a smudge, etc. sometimes occurs in an optical member on an optical path. If a light image without a sample is captured as described above in such a case, an image shown in FIG. 1D is obtained. Defective portions of two points in a bright portion in a central portion are noise caused by dirt, a blemish, a smudge, etc.
If shading correction data is calculated from the image data shown in FIG. 1D in order to execute the shading correction process for the image shown in FIG. 1D, the shading correction data becomes the one shown in FIG. 1E. If the shading correction process is executed for the image data shown in FIG. 1D by using this shading correction data, the image data can be converted into a perfect image of FIG. 1F, from which noise is removed, and which has even brightness.
Also in this case, the shading correction process using the above described shading correction data is executed for image data obtained by capturing the image of a sample placed on the stage, whereby the image data can be converted into sample image data from which noise is removed and which has even brightness.
However, if the sample is actually shot, and the correction process using the shading correction data is executed, the image which should be converted into an image having even brightness is not properly corrected to an image having even brightness. Additionally, a phenomenon that one piece of dirt is corrected and disappears from the image, but another piece of dirt is not corrected occurs. Besides, the quality of the image in the peripheries of the dirt sometimes deteriorates because of the correction.
FIGS. 2A to 2F explain a problem caused by the conventional shading correction made to a captured microscopic image.
As described above, a satisfactory shading characteristic cannot be always obtained in the capturing of a microscopic image because optical members arranged on an optical path of a microscope widely vary. For example, if a decrease in a marginal amount of light is significant as shown in FIG. 2A, the value of the marginal portion of the image in the shading correction data sometimes becomes as large as “2” or “3” as shown in FIG. 2B.
At this time, also the noise of the image after the shading correction process is executed becomes twice or three times in comparison with the image before being processed. The image after being processed, which is shown in FIG. 2C, is an image where the amount of noise in the image is represented by light and dark. In this figure, there is a problem that the quality of the entire image deteriorates due to an increase in the noise although the shading shown in FIG. 2A is corrected.
FIGS. 2D, 2E, and 2F explain a cause for the above described problem. All of FIGS. 2D, 2E, and 2F indicate the signal levels of image data or correction data when pixels are scanned in the middle of the screens shown in FIGS. 2A, 2B, and 2C from the left to the right in the horizontal direction.
As shown in FIG. 2D, the signal level of the original image data including noise (indicated by a jaggy in this figure) indicates a normal value in the neighborhood of a level 200 in the middle portion, but gradually goes down toward the left and the right, and decreases to approximately “56” at both ends.
In the meantime, a shading correction data thus calculated and shown in FIG. 2E, namely, a value corresponding to each pixel gradually increases toward the left and the right from the middle portion that is defined as 1, and indicates a value of approximately “3.6” at both ends in the example shown in FIG. 2E.
If a correction is made by multiplying the respective pixel values of the image data signal shown in FIG. 2D by the shading correction factor, the signal level becomes almost constant in the neighborhood of the normal value of 200 as a whole as shown in FIG. 2F. However, also noise levels at both ends are corrected upward (3.6 times in the example shown in FIG. 2F) along with the signal levels of the image, and an image signal having large noise is formed as a result. This makes the entire image shown in FIG. 2C, especially, the marginal portion of the image deteriorate.
FIGS. 3A, 3B, and 3C explain another problem caused by the conventional shading correction made to a captured microscopic image. Under the optical system shown in FIG. 1D, for example, if image data 3 is obtained by placing a sample of a cell 2 having a nucleus 1 on a stage, and by capturing the image of the sample with a camera as shown in FIG. 3A, the defective portions 4 (4-1, 4-2) of 2 points caused by dirt, a blemish, a smudge, etc., which are shown in FIG. 1D, appear in the image data 3.
In this case, if a correction is made by multiplying shading correction data 5 which is similar to that in the case of FIG. 1E, the defective portions 4 (4-1, 4-2) of the two points should disappear from the image data after being corrected. However, a problem that the upper defective portion 4-2 disappears, but the lower defective portion 4-i still remains occurs as in the image data after being corrected 6 in FIG. 3C.
This is because the degrees of influences received by the defective portions of the two points (such as dirt, a blemish, a smudge, etc.), which are captured without the sample, from the sample differ due to the positions, the sizes, etc. of the two pieces of dirt on the optical path when the observation image is captured with the sample, and accordingly, the levels of brightness of the defective portions of the 2 points differ due to a difference between states where the images of the dirt are formed on the light image of the sample, so that a portion which cannot be corrected with the shading correction data created by being calculated from the light image without the sample is considered to occur.
As described above, it is empirically proved that a satisfactory image is not always obtained in the capturing of a microscopic image even if a shading correction is made by applying the conventional technique unchanged.